This directory (and version of CentOS) is deprecated. For normal users,
you should use /7/ and not /7.4.1708/ in your path. Please see this FAQ
concerning the CentOS release scheme:
https://wiki.centos.org/FAQ/General
If you know what you are doing, and absolutely want to remain at the 7.4.1708
level, go to http://vault.centos.org/ for packages.
Please keep in mind that 7.4.1708 no longer gets any updates, nor
any security fix's.